Highly viscous hydrocarbons present viscosities from about 10,000 to about 500,000 centipoise (cp) at environmental or ambient temperatures (e.g., about 25.degree. C.). Such hydrocarbons include American Petroleum Institute (API) viscous crude oil found in the U.S.A., Canada, China, Russia and Venezuela having, for example, an API value of about 13 degrees or less. The high viscosity of these hydrocarbons introduce several difficulties in their extraction, production, recovery, treatment and/or transportation.
For example, it is difficult to clean and remove residual viscous crude oil which has adhered to wall surfaces of large transport vessel tanks. The residual oil can amount to 5% or as much as 12 tons of oil from the original load, for example, of an oil tanker. Often large quantities of ballast water are used for cleaning and recovering the residual oil. Such recovery and cleaning methods are unappealing given the large quantities of oil and even larger quantities of oil contaminated cleaning water that is produced and then discharged. Thus, the use of water to clean and recover highly viscous residual oil from vessel tanks is both environmentally costly and economically inefficient.
Additionally, it is difficult to extract viscous crude oil from underground sources. Further, because of the high viscosity, transportation of highly viscous crude oil from production fields to refineries or to ports via pipelines becomes extremely difficult. For economically successful extraction, production, recovery, convenient transportation and/or subsequent treatment of highly viscous hydrocarbons, it is necessary that the viscosity of the fluid be reduced, preferably, not to exceed about 500 cp and, more preferably, about 100 cp at operating or ambient temperatures. Further, it is also necessary that the highly viscous hydrocarbons have a reduced pressure drop, preferably, of less than or equal to about 20 psi/mile when transported in a well conduit or a pipeline.
To achieve these pressure drop and viscosity levels, conventional techniques such as heating, dilution with solvents, annular transportation, watery lubrication and encapsulation, have either failed or are too costly. Further, various emulsifying agents along with water have been used to emulsify and effect the viscosity of highly viscous hydrocarbons. However, these emulsification techniques have met with little success in solving the aforesaid problems.
An emulsion is a dispersed system containing at least two immiscible liquid phases. In an emulsion, one immiscible phase forms droplets that are internally dispersed in the second immiscible phase. The second immiscible phase constitutes the continuous phase of the emulsion. It is generally believed that due to excess free energy associated with the surface of the droplets present therein, emulsions are inherently thermodynamically unstable. To minimize the excess free energy, the dispersed droplets, therefore, intrinsically strive to come together and reduce their surface area. If unabated, the droplets floccuolate, ultimately coalesce, grow in size and decrease in number until one large drop is formed. Eventually, the dispersed droplets coalesce or fuse to the degree that the emulsion is substantially destroyed. In effect, the emulsion phases are substantially separated into relatively distinct bulk phases. As non-dispersed bulk phases, one phase of the original emulsion has a minimum of its surface area that is in contact with that of the second phase wherein minimization of the surface free energy is satisfied.
In order to reduce the inherent tendency to coalesce or fuse, an emulsifying agent is added to the immiscible phases to improve emulsion stability. It is generally believed that an emulsifying agent forms a film around each or nearly each dispersed droplet in an emulsion. It is further believed that an emulsifying agent is adsorbed at least as a monolayer at an interface between, for example, a first phase and a second phase. However, the film can be a monolayer, a multi-layer, or a collection of small particles adsorbed at the interface between the phases (i.e., dispersed phase and continuous phase) forming a barrier.
Further, it is likewise believed that the presence of a well-developed charge on the droplet surface significantly aids in promoting the stability of the droplet due to repulsion between approaching drops. Such a potential is more likely to be present when a charged or ionized emulsifying agent is used.
Additionally, it is believed that, by forming a film (or the like) around the dispersed phase of an emulsion, an emulsifying agent lowers the interfacial tension between the emulsion phases and, thereby, lowers the surface free energy of the emulsion. In effect, by lowering the emulsion surface free energy, the emulsifying agent serves to maintain the surface area of the dispersed phase. As a consequence, the emulsifying agent retards and/or eliminates the inherent tendency of the dispersed droplets to coalesce and increases the emulsion stability.
Biosurfactants are a class of emulsifying agents made by microorganisms. Various biosurfactants are produced by microorganisms such as yeasts, fungi, algae and bacteria which yield extracellular metabolites having emulsifying properties. For example, biosurfactant producing microorganisms of the "lipotrehalose" type are Arthrobacter, Brevivacterium, Mycobacterium Kansai, M. Fortuitum, Corynebacterium Diptheriae and Nocardia Esteorides. These microorganisms excrete a metabolite which is a biosurfactant. Typically, the emulsifying agent metabolites have two functional groups, one hydrophilic and the other hydrophobic. The hydrophilic and hydrophobic functional groups increase the metabolite concentrations at the interface between two immiscible phases.
Generally, biosurfactants are classified according to their chemical nature which depends largely upon the genetic make-up of the organism that produced such biosurfactant as well as the culture medium in which the organism was incubated to produce the biosurfactant (e.g., extracellular metabolites, also referenced as bioemulsifiers). By traditional mutagenesis, by genetic engineering and/or by varying the culture medium it is possible to obtain new tenso-active emulsifying agents. For example, it is possible to use recombinant DNA and immobilization techniques to form useful, novel, substantially or relatively non-toxic tenso-active agents for the oil industry.
Some biosurfactants are of a lipo-peptidic and phospho-lipidic nature. Other biosurfactants have a glucolipidic nature. That is, lipids associated to sugars such as trehalose, soforose, rhamnose, diglycosyl diglycerides and other polysaccharides. The presence of such biosurfactants at the interface effect properties such as surface tension, interfacial tension, density, viscosity, electrical conductivity and osmotic pressure. Further, since the chemical structure of biosurfactants is, typically, complex in comparison to synthetic surfactants (which tend to be simple and highly repetitive structures), biosurfactants have the advantage of being able to emulsify, for example, liquid phases with long and ramified chains (e.g., highly viscous API crude oil). Most importantly, such metabolites stabilize and induce emulsions between immiscible phases.
Some of the desirable properties of an emulsifying agent are that the agent should (1) be surface-active and reduce surface tension, (2) be adsorbed, preferably readily and quickly, around dispersed drops as a condensed, non-adherent film which prevents or reduces droplet coalescence, (3) impart to the droplets an adequate electrical potential so that mutual repulsion occurs between droplets of the emulsion, (4) effect the viscosity of the emulsion (e.g., lower the viscosity of the emulsion below that of the most viscous phase) (5) be effective in a reasonably low concentration (e.g., critical micellar concentration) (6) be useful at a low economic cost and (7) be useful at a low environmental cost. However, not all emulsifying agents possess these properties or to the same degree.
For example, fatty alcohols from whale sperm and other less expensive triglycerides (such as coconut oil) have been used as raw materials to produce emulsifying agents. However, these agents produce excessive foam, are difficult to dissolve, require the use of undesirable non-aqueous toxic solvents, are slow to biodegrade and exhibit undesirable toxicity due in part to solvent toxicity.
Furthermore, in terms of the rheological behavior of emulsions, it is often difficult to predict the effect of emulsifying agents upon the viscosity of bulk liquid phases as well as upon the resultant emulsion. This is particularly true because emulsions are difficult systems to study. For example, under shear forces, the droplets of an internal dispersed phase are subject to deform which can unpredictably effect the rheology of the emulsion. Further, with respect to rheology, because of unpredictable interactions between the emulsifying agent, the internal dispersed phase and the continuous phase of the emulsion, it is not possible to make apriori determinations of the rheological effects of an emulsifying agent on an emulsion.
With reference to viscous hydrocarbons, if extraction, recovery, production, transportation and subsequent treatment of highly viscous crude oil from underground sources were made more economically and more environmentally feasible (e.g., cost effective), the benefits would be substantial for countries such as the United States, Canada, China, Russia, Venezuela and other locations where large deposits remain untapped. Thus, it is desirable to form a novel bio-emulsifier and to form a low viscosity emulsion (stabilized with the novel bio-emulsifier) of highly viscous hydrocarbons (e.g., highly viscous crude oil) with water to facilitate economical extraction, production, recovery, treatment and/or transportation thereof. It is further desirable to form a low viscosity emulsion of highly viscous crude oil with water wherein the low viscosity emulsion is formed at a lower economic and lower environmental cost than heretofore possible with conventional techniques.